Fix weight parsing in QBasicUnixFontDatabase

Fix weight parsing in QBasicUnixFontDatabase

First check the usWeightClass in OS/2 font table, then check
the weight byte in panose structure because Nokia Pure Text
fonts only have that set correctly.

Change-Id: Idce2626c8df17ce74ba78b317846cb42c3f1fe84
Reviewed-by: Jørgen Lind
Reviewed-on: http://codereview.qt.nokia.com/2682
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jiang Jiang <jiang.jiang@nokia.com>
Reviewed-on: http://codereview.qt.nokia.com/3460